You had better change the host you use.
Six months ago I got a problem like yours.
I guess the ligates may have no problem.
It is funny thing but you must search new host in any other lab or source.
not in your lab.
Good luck!! and hope this trial.
Tak-Bum Ohn
Department of Biology
Hanyang University
KOREA
Personal E. mail address: ahnss at hitel.kol.co.kr